Carbon to metal bonded assembly and method of making same



Feb. 5, 1963 L. v. PFAENDER 3,076,908

CARBON T0 METAL BONDED ASSEMBLY AND METHOD OF MAKING SAME Filed Feb. 10, 1960 INVENTOR. LAWRENCE V. PFAENDER BY Hilda WW4 A TTOR E Y5 United States Patent 3,076,908 CARBON T METAL BGNDED ASSEMBLY AND METHOD OF MAKING SAME Lawrence V. Pfaender, Toledo, Ohio, assignor to 0wens= Illinois Glass Company, a corporation of ()hio Filed Feb. 10, 1960, Ser. No. 7,762 9 Claims. (Cl. 310-249) motors. The present methods employed by the manufacturers of such carbon brushes require that either a mechanical joint, such as obtained by using a' rivet (see.

U.S. 2,706,261), be used or that a hole be drilled in the carbon brush to receive the pigtail and a special bonding powder be tamped around the pigtailusually requiring special apparatus. While this special powder is unique in that it solidifies under this cold working or tamping so as to unite thepigtail to the carbon brush, no real weld or strong interlock occurs between the carbon brush and solidified powder. Consequently the resulting unitary carbon brush and pigtail are of questionable contact and strength. Moreover, to effect the foregoing connection methods requires considerable equipment and does not provide a low cost installation of a pigtail in the carbon brush. Accordingly it is highly desirable to the industry to provide a new and more economical process whereby the bond between the carbon and metal connector or pigtail is strong and of good contact. n I. 1

It is, therefore, an object of this invention to provide a novel carbon and metal connector or pigtail assembly. A further object of this invention is to provide a carbon brush and connector united by a glass bond in which the entire assembly is characterized by improved strength. A further object of this invention is to provide a carbon brush and connector united by a glass bond in which there is improved contact between the brush and connector. A still further object of this invention is to provide an improved process for making the aforementioned carbon brush and metal connector assembly. These and other objects of this invention will be apparent from the description hereinafter.

The novel process of this invention comprises filling a pre-drilled hole in a carbon block with a conducting devitrifiable solder glass mixture, stirring the glass to remove entrapped air, thereafter inserting the pigtail so as to contact the bottom of the hole, heat drying the glass mixture, and thereafter heating the glass mixture so as to bond the pigtail glass mixture and carbon block into an integral unit.

Other objects and advantages of the foregoing invention will become more apparent from the following description taken in conjunction with the accompanying drawings in which:

FIG. 1 is an elevational view partly in section of one type of conductor to brush connection embodying the present invention;

, 2 FIG. 2 is a cross-sectional view of FIG. 1 along line 2-2;

FIG. 3 is a view similar to FIG. 1 of another type of connection embodying the invention; and

FIG. 4 is a cross-sectional view of FIG. 3 along line 4-4.

Referring to the drawing there is shown in FIG. 1 a

carbon block 1 or brush having rectangular dimensions of 2%" x 1%" x /2" with a circular hole 2 of 4" diameter and /1" depth drilled perpendicularly into the surface having the 1% x /2" dimensions. The hole was then filled with a mixture 3 of seven parts of a devitrifiable solder glass, designated asA, and one part of a silver con,

ducting material in a binder'consisting of 1% percent solution of nitrocellulose in butyl acetate sothat the re sulting mixture could be readily stirred. The filled hole is then stirred so as to'remove any air entrapped the mixture. Thereafter an eight strand copper pigta il 4 was inserted in the middle of the hole until it contacted the bottom thereof. The entire assembly was first heated by means of an ultraviolet lamp for about one hour so as I to dry the mixture; and thereafter placed in an electric oven at 825 F. for about 35 minutes. permitted to cool to 700 F., and the removed from the oven and cooled in air.

The oven was then Although the sealing glass had contracted somewhat in the carbonbrush cavity, the electrical conductivity, contact, andv strength of the bond between the pigtail, glass, and bru h were excellent.

Referring to FIG. 3 there is shown a further embodi ment'of the present invention in-which the procedure employed to make the connector of FIG. 1 was repeated passage in the block into which tlrepigtail 14' was in serted and sealed in place.

The foregoing examples are presented merely as typical illustrations of the present invention, and it is not intended that the invention is to be limited thereby.

Representative of the devitrifiable solder glasses which can be used is the following formulation:

The above formulation is given by way of example, and it is apparent that other devitrifiable solder glasses can be used. In general devitrifiable solder glasses of the following composition ranges can be satisfactorily employed in the present invention:

Percent SiO 1-3 ZnO 7-14 BaO 0-8 PbO -80 B 0 7-10 Moreover, various silver conducting compounds can assembly was then 'respectively, will be found suitable. 'up to 95% of the devitrifiable solder glass can be used .fture is obtained.

silver conducting material which has been found suitable as silver powder having an average grain size of 1 micron.

For most applications a ratio of 87.5% to 12.5% or 7:1 for the dev-itrifiable solder glass and conducting metal, However, amounts where one is concerned mainly with obtaining extremely strong bonds. On the other hand where conductivity is of primary concern the glass component can be reduce-d to 20% or less. In other words from to 80% and more of the conducting metal can be used. Although silver is the preferred conducting metalit is apparent that other conducting materials can be used including tin, iron, platinum, and graphite. In some instances the binder can be dispensed with; and the glass and conducting metal particles can be dry mixed provided a homogeneous mix- In general a firing temperature of 825 to 850 F. fora period of about 30 minutes will be found satisfactory. Where binders are employed, it is evident that organic binders other than nitrocellulose and butyl acetate can be used. It is only necessary that the organic binder :be'one which will (1) readily volatilize during the drying and heating cycles and (2) not react with either the metal or solder glass. Accordingly other organic binders which can be used include gelatin dissolved in water, camphor with cellulose nitrate, dibutyl phthalate with cellulose acetate, and the like.

. It will also be apparent to those skilled in the art that the present invention is applicable to the attachment'of any. metallic. connector or pigtail to a carbon block. However, since one of the widest applications is in the manufacturing of carbon brushes, the examples have been {selected therefrom, and the emphasis has been placed on this area. Moreover, it will be readily evident that where copper connectors or pigtails have been mentioned, the pigtails could also have been fabricated from aluminum, silver, or other electrically conductive metals.

While the illustrative embodiments of the invention have :been described hereinbefore with particularity, it will be understood that various other modifications will be-apparent to and can readily be made by those skilled in the art without departing from the scope and spirit of the invention. Accordingly, it is. not intended that the scope of the claims appended hereto be limited to the eirampl'es and description set forth herein but rather that the claimse construed as encompassing all the features of patenta ble novelty whichreside in the present invention including all features which would be treated as be contbiifed with the devit'rifiable solder glass. One such equivalents thereof by those skilled in the art to which the invention pertains.

What is claimed is: 1. In an electric contact of the type consisting of a 5 conducting carbon block and a conducting metallic pigtail held together by a bonding material, the improvement consisting of employing a conducting devitrifiable solder glass as the bonding material, said glass having the following range in composition Component: Percent SiO 1-3 ZnO 7-14 BaO 0-8 PbO 70-80 12,0 740 2. The contact of claim 1 in which the pigtail is copper. 3. The contact of claim 1 in which the pigtail is silver.

4. The contact of claim 1 in which the pigtail is aluminum.

5. The article of claim 1 in which the conductivity of the solder glass is due to the presence of 5 to 80% by weight of silver.

6. In an electric contact assembly of the type consisting of a carbon brush and metallic pigtail held together by a bonding material which imparts increased strength i and improved electrical conductivity to the assembly, the

improvement consisting of employing a conducting free metal containing solder glass as the bonding material, said glass having the following range in composition tail is silver.

9. The contact assembly of claim 6 in which the pigtail is aluminum.

References Cited in the file of this patent UNITED STATES PATENTS 2,267,571 McDougal Dec. 23, 1941 2,530,217 Bain Nov. 14, 1950 2,849,631 Matz Aug. 26, 1958 

1. IN AN ELECTRIC CONTACT OF THE TYPE CONSISTING OF A CONDUCTING CARBON BLOCK AND A CONDUCTING METALLIC PIGTAIL HELD TOGETHER BY A BONDING MATERIAL, THE IMPROVEMENT CONSISTING OF EMPLOYING A CONDUCTING DEVITRIFIABLE SOLDER GLASS AS THE BONDING MATERIAL, SAID GLASS HAVING THE FOLLOWING RANGE IN COMPOSITION COMPONENT: PERCENT SIO2 1-3 ZNO 7-14 BAO 0-8 PBO 70-80 B2O3 7-10 